A transaminase with β-activity from Variovorax boronicumulans for the production of enantiopure β-amino acids

Enantioselective transamination of amino acids is a great challenge in biotechnology as suitable enzymes with wide substrate spectrum are rare. Here, we present a new transaminase from Variovorax boronicumulans (VboTA, Variovorax boronicumulansω-transaminase) which is specific for β-amino acids. The amino acid sequence of VboTA is similar to an ω-transaminase from Variovorax paradoxus, for which a crystal-structure is available. This similarity is allowing us to classify VboTA as a fold type 1 ω-transaminase (ω-TA). Although both enzymes have a high sequence similarity (86% identities, 92% positives), there are differences in the active center, which allow VboTA to accept a broader substrate spectrum. Both enzymes have also a different temperature stability and temperature optimum. VboTA deaminates the D-form of aromatic β-amino acids, such as β-homophenylalanine and β-phenylalanine as well as aliphatic β-amino acids, such as β-homoalanine and β-leucine. The optimal reaction conditions turned out to be 32 °C and pH 9. Kinetic resolution lead to high enantiomeric excess of 86.6% to >99.9%, depending on the amino donor/acceptor pair. In contrast to many other ω-TAs, VboTA has a broad substrate spectrum and uses both aromatic or aliphatic amino acids. With γ-amino acids as substrates, VboTA showed no activity at all.